The invention relates to the fluid process control industry. More specifically, the invention relates to field devices used in the process control industry and the manner in which those field devices communicate.
Field devices such as transmitters, are used in the process control industry to remotely sense a process variable. Field devices such as actuators, are used by the process control industry to remotely control physical parameters of a process, such as flow rate, temperature, etc. The process variable may be transmitted to a control room from a field device such as a transmitter for providing information about the process to a controller. A controller may then transmit control information to a field device such as an actuator to modify a parameter of the process. For example, information related to pressure of a process fluid may be transmitted to a control room and used to control a process such as oil refining.
Process variable transmitters are used to monitor process variables associated with fluids such as slurries, liquids, vapors and gasses in chemical, pulp, petroleum, gas, pharmaceutical, food and other fluid processing plants. Process variables include pressure, temperature, flow, level, pH, conductivity, turbidity, density, concentration, chemical composition and other fluid properties. Process actuators include control valves, pumps, heaters, agitators, coolers, solenoids, vents and other fluid controlling devices.
One typical prior art technique for transmitting information involves controlling the amount of current flowing through a process control loop. Current is supplied from a current source in the control room and the transmitter controls the current from its location in the field. For example, a 4 mA signal can be used to indicate a zero reading and a 20 mA signal can be used to indicate a full scale reading.
More recently, transmitters have employed digital circuitry which communicates with a controller using a digital signal which is superimposed onto the analog current signal flowing through the process control loop. One example of such a technique is the Hart Foundation HART(copyright) communication protocol. The HART(copyright) protocol and other such protocols typically include a set of commands or instructions which can be sent to the field device to elicit a desired response, such as device control or interrogation.
Fieldbus, another communication protocol, is proposed by the Foundation(trademark) Fieldbus and is directed to defining a communication layer or protocol for transmitting information on a process control loop. The Fieldbus protocol specification is ISA-S50.01-1992, promulgated by the Instrument Society of America in 1992. Fieldbus is a process industry communications protocol described in Fieldbus Technical Overview Understanding Foundation(trademark) fieldbus technology (1998) available from Rosemount Inc. in Eden Prairie, Minn. Some protocols comparable to Fieldbus include Controller Area Network (CAN), Lonworks, and Profibus. In the Fieldbus protocol, the current flowing through the process control loop is not used to transmit an analog signal. Instead, all information is digitally transmitted. Further, the Fieldbus protocol allows field devices to be configured in a multi-drop configuration in which more than one field device is connected on the same process control loop.
The HART(copyright) protocol and more recently the Fieldbus protocol have been relatively effective at communicating process information over process control loops. Current process control systems generally include many field devices and actuators coupled to a given process control loop which is in turn coupled to a controller. If it is desirable to provide process control information on an enterprise-wide level, such as throughout an entire company, the controller itself is coupled to an enterprise-wide data network, such as an Ethernet data network, and the controller provides information about the process to the enterprise.
The invention includes a process device which is adapted to couple to a process control loop and communicate on the process control loop. Communication on the process control loop is effected in accordance with an internet protocol.
A process communication device is also provided which is adapted to couple to a process control loop, and the Internet. The process communication device provides process control information received from the process control loop, to the internet. Conversely, the process communication device also provides information received from the internet to the process control loop.